1. Field of the Invention
The present invention relates to information communication systems. More particularly, the present invention relates to a system and method for modifying output power of an information communication system.
2. Background Information
Automatic gain control (AGC) circuits are widely used in devices such as radio transceivers to, for example, compensate for variations in received signal strength. In transmitting information, the transceivers can be required to change gain very rapidly. For example, in certain wireless networking application, an access point transceiver must change gain from one packet to the next as successive packets are transmitted to different receivers over channels having different channel gains.
An AGC circuit generates a control signal responsive to signal strength or output power level, and can use this control signal to control the gain of a variable gain amplifier (VGA) that amplifies the signal input to the VGA. The amplified level of the input signal can be kept within the range of linear operation of other circuit elements that process the resulting signal.
One problem in this type of AGC circuit is that the AGC circuit may be employed in a product having different amplification requirements for different signals passing through transceiver. For a packet-based system, in which the signal strength detection and subsequent VGA gain adjustment occur once per packet, it can take several packets before the AGC circuit settles to the final target power, resulting in a slow adaptation speed. A further problem in this type of AGC circuit is that the gain control characteristics of the VGA itself may change due to, for example, temperature changes of the integrated circuit that comprises the transceiver. Excessive drift in the gain control characteristics of the VGA can result in the failure to keep the different amplified signals within the necessary range or to provide the appropriate amplification for each of the given signals.